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The Basic Components Booting Up 1 Bootstrap CMOS basic boot parameters (boot device ID, boot sector location and size, etc.) stored in low-power memory loaded from sector 0 of boot device; loads more sophisticated loader program RAM Bootstrap Loader OS Loader loads OS kernel from boot device ROM POST BIOS Power-On Self-Test fundamental hardware checks before any other software is installed Boot Device Basic I/O System knows just enough to perform necessary data transfers Computer Science Dept Va Tech Jan 2008 Operating Systems ©2003-08 McQuain Data Flow Booting Up 2 RAM Boot Device Bootstrap ROM Loader POST OS BIOS CMOS Computer Science Dept Va Tech Jan 2008 Operating Systems ©2003-08 McQuain The Hardware Process Booting Up 3 RAM Boot Device Bootstrap ROM Power Up Loader POST OS BIOS CMOS Computer Science Dept Va Tech Jan 2008 Operating Systems ©2003-08 McQuain Bootstrap Program FIXED_LOC: Booting Up 4 # bootstrap loader entry point load R1, =0 load R2, =LENGTH_OF_TARGET # next instructions copy a block from BOOT_DISK to memory: read loop: load BOOT_DISK, BUFFER_ADDRESS R3, [BUFFER_ADDRESS, R1] store R3, [FIXED_DEST, R1] incr R1 bleq R1, R2, loop br FIXED_DEST Computer Science Dept Va Tech Jan 2008 Operating Systems ©2003-08 McQuain